1. Field of the Invention
The present invention generally relates to electronic packaging and printed circuit boards. More particularly, the present invention provides a technique for adjusting clearance hole size for impedance control in multilayer electronic packaging and printed circuit boards.
2. Related Art
As the demand for electronic systems supporting high speed signals continues to increase, there is a need to design chip to chip interconnect hardware using wave propagation physics such that signals are not distorted when traveling through a chip, electronic package, and/or printed circuit board. Currently, in multilayer electronic packages or printed circuit boards, a clearance hole in the power or ground plane is provided around a signal via interconnect and is manufactured purely based on mechanical considerations. Unfortunately, in many cases, the size of the clearance hole around the signal via interconnect is too small, which causes an increase in localized capacitance for the signal via interconnect. The higher the number of layers the signal via interconnect traverses in a multilayer structure, the larger the value of the unwanted capacitance. The extra capacitance causes a lowering of the characteristic impedance of the signal line connection, which is typically optimally designed to be 50 Ohms (100 Ohms differential impedance). Conversely, if the size of the clearance hole around the via signal interconnect is too large, the characteristic impedance of the signal line connection may increase to a value over the optimum value of 50 Ohms (100 Ohms differential impedance). Deviations in the characteristic impedance due to such localized capacitance variations cause reflection of the propagating signal at those points and a higher return loss (i.e., the ratio of the reflected signal to the incident signal). Accordingly, there is a need for a technique for adjusting clearance hole size for impedance control in multilayer electronic packaging and printed circuit boards that obviates these and other problems associated with the prior art.